In recent years, positive nickel electrodes intended for alkaline batteries, such as Ni-Cd, Ni-Zn, Ni-Fe, etc., have been developed by two methods.
The first and earlier method comprises packing the active material, namely hydroxide Ni(OH).sub.2, mixed with an additional conductor into a metal container of which the walls are perforated so that the electrolyte is able to impregnate the active material without the active material being able to escape from the container. Although electrodes such as these can be produced at relatively low cost, they are attended by the disadvantage that they have unfavourable weight characteristics (Ah/kg) and are unsuitable for severe charging and discharging conditions.
Progress was also made by development of the process for making electrodes having sintered or fibrous support in which the active material is introduced by chemical or electrochemical precipitation. Electrodes of this type were found to be capable of restoring a significant fraction of their nominal capacity even when they are subjected to discharging rates as rapid as 17 C (discharge in 1/17th of an hour).
However, it must be emphasized that impregnation by chemical precipitation takes a considerable time (several tens of hours). Electrochemical impregnation is advantageous in this regard insofar as it can be carried out in about 1 hour for surface capacities of the order of 40 mAh/cm.sup.2.
Over the last decade, numerous efforts have been made to develop a continuous process for introducing the active material into a support by mechanical filling with paste. U.S. Pat. Nos. 4,217,939 and 4,251,603 (Matsushita) and FR-PS 2 618 949 (Sanyo) describe processes for the introduction of a paste based on Ni(OH).sub.2 into three-dimensional structures of the foam type. In addition, it is clear from many publications, particularly those cited above and French Patent No. 2 567 326 (Wonder), that a good yield of active material can only be obtained providing an additionnal conductor, generally Ni powder, is added to the Ni hydroxide.
Japanese patents JP-A-52036732 (Matsushita) and JP-A-6251157 (Shin Kobe Electric Match) describe the use of a paste based on nickel hydroxide and nickel carbonyl or metallic nickel containing cobalt hydroxide.
In the case of Wonder, the Ni(OH).sub.2 powder is accompanied by a conductive powder of nickel carbonyl or graphite. Finally, the advantage of immersing the electrode in cobalt sulfate with regard to the charging efficiency of Ni(OH).sub.2 is also mentioned.